Method For Manufacturing Semiconductor Device

ABSTRACT

A method for manufacturing semiconductor device according to the present invention comprises a first film forming step of forming, on a concave and convex portion formed by an element on a semiconductor substrate, an oxidation preventive layer which prevents permeation of moisture into the element; a second film forming step of forming, on this oxidation preventive layer, an expansion layer which can be oxidized and expanded by a heat treatment in an oxidation atmosphere; a third film forming step of forming, on this expansion layer, an insulating film which can be fluidized by the heat treatment in the oxidation atmosphere; and an expansion step of subjecting, to the heat treatment in the oxidation atmosphere, the semiconductor substrate on which the oxidation preventive layer, the expansion layer and the insulating film have been formed, to fluidize the insulating film and to oxidize and expand the expansion layer, thereby eliminating bubbles generated in the insulating film.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a method for manufacturing asemiconductor device including an insulating film on a semiconductorsubstrate (wafer). More particularly, it relates to a method formanufacturing semiconductor device which can completely eliminate voids(bubbles) generated in the insulating film or open pores generated owingto insufficient filling-in of the insulating film.

2. Description of the Related Art

For example, in steps of manufacturing a semiconductor device, an MOSFETgate electrode is formed on a semiconductor substrate to protrudetherefrom, whereby a concave portion is formed between the gateelectrode and a gate electrode adjacent to the electrode, and a concaveportion, a convex portion and a stepped portion (trench) are made in thegate electrode and between the gate electrodes. When this steppedportion enlarges, there occurs focus deviation during drawing of awiring pattern by exposure. In a case where wiring lines are formed tointersect with one another, a lap portion of an intersecting portionbecomes thin, and this causes disconnection. Such problems are generatedwhich result in defects of the semiconductor device. To solve theproblems, as a method of eliminating such stepped portion, an interlayer dielectric such as a BPSG film or a PSG film is formed on thestepped portion by a chemical vapor deposition (CVD), and the surface ofthis inter layer dielectric is flattened by a certain method.

In recent years, as there have progressed the miniaturization and highdensification of semiconductor devices with high integration andcapacity enlargement thereof, an aspect ratio (ratio of adepth-direction dimension with respect to a lateral dimension of astructure) of each structure rises, and the stepped portion of thestructure tends to enlarge in a preparing step. Therefore, there rises aprobability that voids (bubbles) are generated in the insulating filmduring formation of the above inter layer dielectric, and open pores aresometimes generated in the insulating film owing to unevenness of theformation of the insulating film in the trench or lack of a filmformation amount (film formation defect). FIGS. 1A and 1B show sectionalshapes of a semiconductor device in the process of the manufacturing ofa conventional semiconductor device, FIG. 1A shows a case where a void53 is generated in an inter layer dielectric 52 formed on a concave andconvex portion 51 formed by an element on a semiconductor substrate 50,and FIG. 1B shows a case where an open pore 54 is generated in the interlayer dielectric 52. It is to be noted that in FIGS. 1A and 1B,reference numeral 55 denotes a barrier layer.

Heretofore, the semiconductor substrate on which the inter layerdielectric has been formed is subjected to a heat treatment at atemperature of 900° C. in an inert gas atmosphere under a normalpressure (0.1 MPa) or subjected to a heat treatment at a temperatureslightly below 900° C. in the atmosphere containing oxygen or watervapor under the normal pressure, thereby fluidizing (reflowing) theinsulating film to thereby flatten the film. By this reflow treatment,the voids or the open pores generated in the insulating film have beeneliminated. As prior arts associated with this method, the followingpatent documents 1 and 2 are disclosed.

The “method for flattening insulating film of semiconductor device” ofPatent Document 1 has a purpose of effectively conducting a reflowtreatment on a BPSG film of a semiconductor device at comparatively lowtemperature in a short period of time. In a method in which theinsulating film formed on the concave and convex surface of a substrateof the semiconductor device is flattened by thermal reflow, the thermalreflow is performed in the atmosphere containing oxygen or water vaporunder a pressure of 0.3 MPa or more. Moreover, according to this method,the quantity of oxygen to be diffused on the insulating film and thediffusion speed increase, and excellent reflow of the BPSG film isaccomplished at a low temperature for a short period of time as comparedwith a conventional method.

The “method for manufacturing semiconductor device” of Patent Document 2has a purpose of obtaining flatness which is sufficient for performing alow-temperature treatment. After an element is formed on a semiconductorsubstrate, a silicon nitride film is formed on this element. On thisfilm, a BPSG film containing boron and phosphorus is formed, and furtheron this film, an SOG film containing at least one of boron andphosphorous is formed by a coating method. Then, the substrate isheat-treated in a high-pressure atmosphere containing water vapor.Therefore, the SOG film is gelatinized and flattened by a high externalpressure which is applied to the film itself.

[Patent Document 1]

Japanese Unexamined Patent Publication No. 5-67607

[Patent Document 2]

Japanese Unexamined Patent Publication No. 10-275805

In the above “method for flattening insulating film of semiconductordevice” of Patent Document 1, the heat treatment can be performed at800° C. which is lower than a conventional reflow treatment temperature.In the “method for manufacturing semiconductor device” of PatentDocument 2, the reflow treatment temperature can be set to 700° C. orless. It can be expected that the insulating film can be fluidized bythe reflow treatment to eliminate the voids or the open pores generatedin the insulating film. However, since the heat treatment temperature of700° C. to 800° C. as in Patent Documents 1 and 2 adversely affectscharacteristics of the element to be miniaturized, there is a demand fora further decrease of the treatment temperature to reduce damages due tothe heat treatment in further integrating the semiconductor device. Evenin the treatment at the high temperature, in which a high fluidity isobtained, the voids remain sometimes without being completelyeliminated, depending on a position where the voids have been generatedor a size of the voids. The remaining voids might cause a device defect.Especially as the size of the voids is decreased, an effect produced bybuoyancy during the fluidization deteriorates, and this increasinglyraises a possibility that the voids remain. In a case where the openpores are generated in the insulating film, the surface of the openpores is flattened by surface tension of the insulating film during thereflow treatment, but the open pores are not closed, or the concave andconvex portion (trenches) is not filled in.

SUMMARY OF THE INVENTION

The present invention has been developed in order to solve the aboveproblems. That is, an object of the present invention is to provide amethod for manufacturing a semiconductor device, in which voids in aninter layer dielectric can completely be eliminated at a heat treatmenttemperature that is lower than before, and further open pores generatedin the inter layer dielectric can be filled in.

To achieve the object of the present invention, according to a firstaspect of the invention, there is provided a method for manufacturingsemiconductor device, including: a first film forming step of forming,on a concave and convex portion formed by an element on a semiconductorsubstrate, an oxidation preventive layer which prevents permeation ofmoisture into the element; a second film forming step of forming, onthis oxidation preventive layer, an expansion layer which can beoxidized and expanded by a heat treatment in an oxidation atmosphere; athird film forming step of forming, on this expansion layer, aninsulating film which can be fluidized by the heat treatment in theoxidation atmosphere; and an expansion step of subjecting, to the heattreatment in the oxidation atmosphere, the semiconductor substrate onwhich the oxidation preventive layer, the expansion layer and theinsulating film have been formed, to fluidize the insulating film and tooxidize and expand the expansion layer, thereby eliminating bubblesgenerated in the insulating film.

In a second aspect of the invention, which is a preferable embodiment ofthe first aspect of the invention, the expansion layer is made of apolycrystalline silicon, an amorphous silicon or a silicide.

In a third aspect of the invention, which is a preferable embodiment ofthe first aspect of the invention, the expansion layer is made ofaluminum, tantalum or an alloy of them.

In a fourth aspect of the invention, which is a preferable embodiment ofthe first aspect of the invention, the insulating film is a siliconoxide film containing at least one of phosphorus, arsenic, boron,fluorine and a halide.

In a fifth aspect of the invention, which is a preferable embodiment ofthe first aspect of the invention, the oxidation preventive layer isformed of a silicon nitride film.

In a sixth aspect of the invention, which is a preferable embodiment ofthe first aspect of the invention, a pressure of the oxidationatmosphere in the expansion step is atmospheric pressure or more, and aheat treatment temperature is 400° C. to 800° C.

According to a seventh aspect of the invention, there is provided amethod for manufacturing semiconductor device, comprising a first filmforming step of forming, on a concave and convex portion formed by anelement on a semiconductor substrate, an oxidation preventive layerwhich prevents permeation of moisture into the element; a second filmforming step of forming, on this oxidation preventive layer, anexpansion flow layer which can be oxidized, expanded and fluidized by aheat treatment in an oxidation atmosphere and which has an insulatingproperty; and an expansion step of subjecting, to the heat treatment inthe oxidation atmosphere, the semiconductor substrate on which theoxidation preventive layer and the expansion flow layer have beenformed, to oxidize, expand and fluidize the expansion flow layer,thereby eliminating bubbles or open pores generated in the expansionflow layer.

In an eighth aspect of the invention, which is a preferable embodimentof the seventh aspect of the invention, the expansion flow layer is madeof a polycrystalline silicon or an amorphous silicon containing at leastone of boron, phosphorus and fluorine.

In a ninth aspect of the invention, which is a preferable embodiment ofthe seventh aspect of the invention, the oxidation preventive layer isformed of a silicon nitride film.

In a tenth aspect of the invention, which is a preferable embodiment ofthe seventh aspect of the invention, a pressure of the oxidationatmosphere in the expansion step is atmospheric pressure or more, and aheat treatment temperature is 400° C. to 800° C.

According to the first to sixth aspects of the invention, the oxidationpreventive layer is formed on the concave and convex portion formed bythe element on the semiconductor substrate, the expansion layer isformed on the oxidation preventive layer, the insulating film is formedon the expansion layer, and the semiconductor substrate on which theyhave been formed is subjected to the heat treatment in the high-pressureoxidation atmosphere. The insulating film is fluidized, and theexpansion layer is oxidized and expanded, thereby promoting thefluidization of the insulating film. In consequence, the voids (bubbles)generated in the insulating film can completely be eliminated.

Moreover, according to the seventh to tenth aspects of the invention,the oxidation preventive layer is formed on the concave and convexportion formed by the element on the semiconductor substrate, theexpansion flow layer is formed on the oxidation preventive layer, andthe semiconductor device on which they have been formed is subjected tothe heat treatment in the high-pressure oxidation atmosphere, and theexpansion flow layer is expanded and fluidized, whereby the voids(bubbles) generated in the expansion flow layer can completely beeliminated. Even in a case where the open pores are generated owing toinsufficient filling-in of the expansion flow layer, the open pores arefilled in owing to effects of the expansion and fluidization, and theopen pores can therefore be eliminated.

In the conventional reflow treatment in which a fluidizing effect onlyis expected, a fluid resistance increases, when the voids become small.Therefore, it has been necessary to raise a treatment temperature orlengthen a treatment time. However, in a case where the expansion layeris used for promoting the fluidization of the insulating film as in thefirst to tenth aspects of the invention, the heat treatment temperatureand time depend on expansion of the expansion layer. Therefore, as thevoids become small, the expansion of the expansion layer for eliminatingthe voids may be small. Therefore, it is possible to lower the treatmenttemperature, or shorten the treatment time. Even in a case where theexpansion flow layer is expanded and fluidized, the heat treatmenttemperature and time depend on the expansion of the expansion flowlayer. Therefore, similarly it is possible to lower the treatmenttemperature, or shorten the treatment time.

Therefore, according to the method of manufacturing the semiconductordevice of the present invention, it is possible to obtain effects thatthe treatment temperature can be set to be lower than before, thesemiconductor device can be manufactured without any voids or open poresin the insulating film, and yield of the device can be enhanced.

Other objects and advantageous characteristics of the present inventionwill be apparent from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing prior arts;

FIGS. 2A to 2C are diagrams showing sectional shapes of a semiconductordevice to which there is applied the method for manufacturingsemiconductor device in a first embodiment of the present invention;

FIG. 3 is a diagram showing dependence of oxide film thicknesses of apolycrystalline silicon and single crystal silicon on a treatment time;

FIG. 4 is a diagram showing the dependence of the thickness of thesingle crystal silicon oxide film on a treatment temperature;

FIG. 5 is a diagram showing the dependence of the speed of the singlecrystal silicon oxide film on a treatment pressure;

FIGS. 6A and 6B are diagrams showing a behavior in which voids in aninsulating film are eliminated by the method for manufacturingsemiconductor device in the first embodiment of the present invention:

FIGS. 7A to 7E are diagrams showing sectional shapes of a semiconductordevice to which there is applied the method for manufacturingsemiconductor device in a second embodiment of the present invention;and

FIGS. 8A and 8B are diagrams showing a behavior in which open pores ofan expansion flow layer are eliminated by the method for manufacturingsemiconductor device in the second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention will be described hereinafter indetail with reference to the accompanying drawings. It is to be notedthat in each drawing, the same part is denoted with the same referencenumeral, and redundant description is omitted.

First, there will be described the method for manufacturingsemiconductor device in a first embodiment of the present invention. Themethod for manufacturing semiconductor device in the first embodiment ofthe present invention includes: a first film forming step of forming anoxidation preventive layer on a concave and convex portion formed by anelement on a semiconductor substrate; a second film forming step offorming an expansion layer; a third film forming step of forming aninsulating film; and an expansion step of subjecting, to a heattreatment, the semiconductor substrate on which they have been formed,thereby expanding the expansion layer. The respective steps will bedescribed hereinafter.

FIGS. 2A to 2C show sectional shapes of the semiconductor device towhich there is applied the method for manufacturing semiconductor devicein the first embodiment of the present invention. First, as shown inFIG. 2A, the first film forming step is performed to form an oxidationpreventive layer 2 as a first layer by a low-pressure chemical vapordeposition (hereinafter referred to as “LPCVD”) on a concave and convexportion 1 (trench) formed by a wiring structure (element) such as a gateinsulating film or a gate electrode formed on a semiconductor substrate11. In the present embodiment, a magnitude of the trench of the concaveand convex portion 1 indicates a width of 1 μm and a depth of 2.5 μm,and the oxidation preventive layer 2 having a thickness of 150 nm wasformed on this portion. This oxidation preventive layer 2 is formed of,for example, a silicon nitride film, and functions as a protective film(barrier layer) for preventing permeation of moisture due to a treatmentof the subsequent step into the element.

Next, as shown in FIG. 2B, the second film forming step is performed byLPCVD to form, on the oxidation preventive layer 2 as the first layer,an expansion layer 3 as a second layer which can be oxidized andexpanded by a heat treatment in an oxidation atmosphere. The expansionlayer 3 is formed so that a thickness of the layer becomes ½ or more ofa width of each void which would finally be generated in an insulatingfilm 4 described later. In the present embodiment, the expansion layer 3having a thickness of 100 nm was formed. This expansion layer 3 ispreferably a film made of a polycrystalline silicon, an amorphoussilicon or a silicide. The layer may be a film made of aluminum,tantalum or an alloy of them. Furthermore, in addition to the aboveexpansion layer, it is possible to adopt all substances that have aproperty of being oxidized to expand in the oxidation atmosphere.

Next, as shown in FIG. 2C, the third film forming step is performed byan atmospheric-pressure chemical vapor deposition (hereinafter referredto as “APCVD”) to form, on the expansion layer 3 as the second layer,the insulating film 4 as a third layer to such a degree as to fill inthe concave and convex portion. This insulating film 4 is preferably asilicon oxide film (a BPSG film, a PSG film or the like) containing atleast one of phosphorus, arsenic, boron, fluorine and a halide. At thistime, a void 5 (bubble) is generated in the insulating film 4 as shownin the drawing.

Next, the expansion step is performed to subject the semiconductorsubstrate 11 having the formed first to third layers to a heat treatmentin an atmosphere (oxidation atmosphere) containing oxygen or watervapor, whereby the expansion layer 3 is oxidized and expanded.

Here, FIG. 3 shows dependence of oxide film thicknesses of apolycrystalline silicon and single crystal silicon on a oxidationtreatment time. The abscissa indicates an oxidation treatment time[min], and the ordinate indicates an oxide film thickness [nm]. In thefigure, “p-Si” indicates the polycrystalline silicon, and “c-Si (100)”indicates the single crystal silicon (100). A heat treatment wasperformed in the atmosphere containing water vapor under conditions thata temperature and a pressure were 600° C. and 2 MPa, respectively. Fromthis result, it is seen that the thicknesses of oxide films of both ofthe polycrystalline silicon and the single crystal silicon tend toincrease in proportion to an oxidation treatment time.

FIG. 4 shows dependence of the thickness of the single crystal siliconoxide film on an oxidation treatment temperature, the abscissa indicatesan oxidation treatment time [min], and the ordinate indicates the oxidefilm thickness [nm]. In the figure, “white circle”, “black square” and“black triangle” indicate treatment temperatures, respectively, “whitecircle” indicates 600° C., “black square” indicates 580° C., and “blacktriangle” indicates 550° C. Any of heat treatments was performed in theatmosphere containing water vapor under pressure conditions of 2 MPa.From this result, it is seen that the thickness of the oxide film ofsingle crystal silicon tends to exponentially increase with respect tothe oxidation treatment temperature.

FIG. 5 shows the dependence of the oxidation speed of the single crystalsilicon oxide film on an oxidation pressure, the abscissa indicates anoxidation treatment pressure [MPa], and the ordinate indicates theoxidation speed [nm/min]. The heat treatment was performed in theatmosphere containing water vapor under heating conditions at 600° C.From this result, it is seen that the thickness of the oxide film ofsingle crystal silicon tends to increase in proportion to the oxidationtreatment pressure.

As one example of the heat treatment, the heat treatment was performedin the atmosphere containing water vapor under pressure conditions of 2MPa and heating conditions at 600° C. In a case where an oxidation rateof the polycrystalline silicon was about 46 nm per hour, an oxidationrate of the amorphous silicon was about 24 nm per hour. When a voiddiameter was about 50 nm, and the expansion layer was a polycrystallinesilicon layer, about two hours were required. When a void diameter wasabout 50 nm, and the expansion layer was an amorphous silicon layer,about four hours were required.

Therefore, based on these results, it is preferable that in theexpansion step, the heat treatment is performed in the oxidationatmosphere under pressure conditions of atmospheric pressure (about 0.1MPa) or more and under heating conditions at 400° C. to 800° C. From theresult of FIG. 5, since the oxidation speed of the expansion layer 3 isproportional to the treatment pressure, a specific treatment pressure isset to a pressure which is not below a practical treatment time from aviewpoint of productivity or the like. This heat treatment is performedto oxidize the expansion layer 3 formed as the second layer in ahigh-pressure oxidation atmosphere. When the expansion layer 3 is apolycrystalline silicon layer, the layer changes to silicon oxide, andthe oxidized polycrystalline silicon layer expands until the thicknessis approximately doubled. At this time, the expansion layer 3 expands tothereby compress an insulating film 4 such as the BPSG film that is thethird layer heated to lower viscosity and fluidized, and the void 5 inthe insulating film 4 contracts as shown in FIG. 6A. Moreover, in afinal stage of the heat treatment, the expansion layer 3 expands,whereby the void completely disappears as shown in FIG. 6B.

Moreover, in this stage, impurities from an insulating film 4 such asthe BPSG film containing the impurities diffuse to the oxidized andexpanded expansion layer 3, finally form a layer similar to theinsulating film 4, and function as a void-free inter layer dielectric.For example, when the expansion layer 3 is the polycrystalline silicon,and the insulating film 4 is a BPSG film, the polycrystalline silicon isoxidized to form silicon oxide, and onto this film, the impurities fromthe BPSG film diffuse to finally form the BPSG film.

As described above, according to the first embodiment of the presentinvention, the oxidation preventive layer 2 is formed on the concave andconvex portion 1 formed by the element on the semiconductor substrate11, on the layer, the expansion layer 3 is formed, and on the layer, theinsulating film 4 is formed. Moreover, the semiconductor substrate 11 onwhich they have been formed is subjected to the heat treatment in thehigh-pressure oxidation atmosphere to fluidize the insulating film 4 andto oxidize and expand the expansion layer 3. In consequence, since thefluidization of the insulating film 4 is promoted, it is possible toobtain an effect that the void 5 (bubble) generated in the insulatingfilm 4 can completely be eliminated. As a result, yield of the devicecan be enhanced.

In the conventional reflow treatment in which a fluidizing effect onlyis expected, as the void becomes small, a fluid resistance increases.Therefore, it is necessary to raise the treatment temperature orlengthen the treatment time. However, in a case where the expansionlayer 3 is used for promoting the fluidization of the insulating film 4as in the present invention, the temperature and time of the heattreatment depend on expansion of the expansion layer 3. Therefore, asthe void 5 becomes small, the expansion of the expansion layer 3 foreliminating the void 5 may be reduced. In consequence, it is possible tolower the treatment temperature or shorten the treatment time.

Next, there will be described the method for manufacturing semiconductordevice in a second embodiment of the present invention. The method formanufacturing semiconductor device in the second embodiment of thepresent invention includes: a first film forming step of forming anoxidation preventive layer on a concave and convex portion 1 formed byan element on a semiconductor substrate 11; a second film forming stepof forming an expansion flow layer; and an expansion step of subjectingthe semiconductor substrate 11 having these formed films to a heattreatment, thereby expanding the expansion flow layer. The respectivesteps will be described hereinafter.

FIGS. 7A to 7E show sectional shapes of the semiconductor device towhich there is applied the method of manufacturing the semiconductordevice in the second embodiment of the present invention. First, asshown in FIG. 7A, the first film forming step is performed to form anoxidation preventive layer 2 as a first layer by an LPCVD on the concaveand convex portion 1 formed by the element on the semiconductorsubstrate 11. This oxidation preventive layer 2 is similar to that ofthe first embodiment.

Next, as shown in FIG. 7B, the second film forming step is performed bythe LPCVD to such a degree as to fill in the concave and convex portion1, thereby forming, on the oxidation preventive layer 2 as the firstlayer, an expansion flow layer 6 as a second layer which can beoxidized, expanded and fluidized by a heat treatment in an oxidationatmosphere and which has an insulating property. At this time, when avoid 5 (bubble) is generated in the expansion flow layer 6 as shown inthe figure, or when the concave and convex portion 1 is insufficientlyfilled with the expansion flow layer 6 as shown in FIG. 7C, an open pore7 is generated. This expansion flow layer 6 is preferably made of thepolycrystalline silicon (doped polycrystalline silicon) containing atleast one of boron, phosphorus and fluorine or an amorphous silicon(doped amorphous silicon). As the expansion flow layer 6, in addition tothe above layer, it is possible to adopt all substances that areoxidized, expanded and fluidized in the oxidation atmosphere and thatare oxidized to have an insulating property.

Next, the expansion step is performed to subject the semiconductorsubstrate 11 having the formed first and second layers thereon to a heattreatment in an oxidation atmosphere, thereby expanding and fluidizingthe expansion flow layer. In the expansion step, in the same manner asin the first embodiment, it is preferable that the heat treatment isperformed in the oxidation atmosphere under pressure conditions ofatmospheric pressure (about 0.1 MPa) or more and under heatingconditions at 400° C. to 800° C. This heat treatment is performed tooxidize the expansion flow layer 6 formed as the second layer in ahigh-pressure oxidation atmosphere. When the expansion flow layer 6 is adoped polycrystalline silicon or a doped amorphous silicon, the layerchanges to silicon oxide (BSG, PSG, BPSG or the like) containingphosphorus, boron or the like. In this oxidation process, the expansionflow layer 6 expands. Moreover, the heat treatment is performed tothereby lower viscosity of the layer and fluidize the layer. At thistime, the expansion flow layer 6 expands until the thickness isapproximately doubled at maximum.

In consequence, the void 5 in the expansion flow layer 6 is compressedto contract as shown in FIG. 7D, and in a final stage of the heattreatment, the void 5 completely disappears as shown in FIG. 7E. Even ina case where the open pore 7 is generated, the expansion flow layer 6 issubjected to the heat treatment, thereby expanding and fluidizing theexpansion flow layer. Accordingly, after the surface of the open pore 7is flattened as shown in FIG. 8A, the pore shifts to a void 8 as shownin FIG. 8B. Moreover, thereafter the void is compressed to contract inthe same manner as in FIG. 7D, and finally filled in completely in thesame manner as in FIG. 7E, and the void 8 disappears.

As described above, according to the method for manufacturingsemiconductor device in the second embodiment of the present invention,the oxidation preventive layer 2 is formed on the concave and convexportion 1 formed by the element on the semiconductor substrate 11, andon the layer, the expansion flow layer 6 is formed. Moreover, thesemiconductor device on which these films have been formed is subjectedto the heat treatment in the high-pressure oxidation atmosphere toexpand and fluidize the expansion flow layer 6, whereby it is possibleto obtain an effect that the void 5 (bubble) generated in the expansionflow layer 6 can completely be eliminated. Even in a case where the openpore 7 is generated because the concave and convex portion 1 isinsufficiently filled with the expansion flow layer 6, the open pore 7is filled in owing to the effects of expansion and fluidization, wherebyit is possible to obtain an effect that the open pore 7 can beeliminated. As this result, yield of the device can be enhanced.

Moreover, in a case where the expansion flow layer 6 is expanded andfluidized, in the same manner as in the first embodiment, thetemperature and time of the heat treatment depend on the expansion ofthe expansion flow layer 6. Therefore, as the void 5 becomes small, theexpansion of the expansion layer for eliminating the void 5 may bereduced. In consequence, it is possible to similarly lower the treatmenttemperature or shorten the treatment time.

It is to be noted that the method for manufacturing semiconductor deviceof the present invention has been described in accordance with thepreferable embodiments, but it would be understood that the scopecontained in the present invention is not limited to the embodiments.Conversely, the scope of the present invention includes allimprovements, modifications and equivalents included in the appendedclaims.

1. A method for manufacturing semiconductor device, comprising: a firstfilm forming step of forming, on a concave and convex portion formed byan element on a semiconductor substrate, an oxidation preventive layerwhich prevents permeation of moisture into the element; a second filmforming step of forming, on the oxidation preventive layer, an expansionlayer which can be oxidized and expanded by a heat treatment in anoxidation atmosphere; a third film forming step of forming, on theexpansion layer, an insulating film which can be fluidized by the heattreatment in the oxidation atmosphere; and an expansion step ofsubjecting, to the heat treatment in the oxidation atmosphere, thesemiconductor substrate on which the oxidation preventive layer, theexpansion layer and the insulating film have been formed, to fluidizethe insulating film and to oxidize and expand the expansion layer,thereby eliminating bubbles generated in the insulating film.
 2. Themethod for manufacturing semiconductor device according to claim 1,wherein the expansion layer is made of a polycrystalline silicon, anamorphous silicon or a silicide.
 3. The method for manufacturingsemiconductor device according to claim 1, wherein the expansion layeris made of aluminum, tantalum or an alloy of them.
 4. The method formanufacturing semiconductor device according to claim 1, wherein theinsulating film is a silicon oxide film containing at least one ofphosphorus, arsenic, boron, fluorine and a halide.
 5. The method formanufacturing semiconductor device according to claim 1, wherein theoxidation preventive layer is formed of a silicon nitride film.
 6. Themethod for manufacturing semiconductor device according to claim 1,wherein a pressure of the oxidation atmosphere in the expansion step isatmospheric pressure or more, and a temperature of the heat treatment is400° C. to 800° C.
 7. A method for manufacturing semiconductor device,comprising: a first film forming step of forming, on a concave andconvex portion formed by an element on a semiconductor substrate, anoxidation preventive layer which prevents permeation of moisture intothe element; a second film forming step of forming, on the oxidationpreventive layer, an expansion flow layer which can be oxidized,expanded and fluidized by a heat treatment in an oxidation atmosphereand which has an insulating property; and an expansion step ofsubjecting, to the heat treatment in the oxidation atmosphere, thesemiconductor substrate on which the oxidation preventive layer and theexpansion flow layer have been formed, to oxidize, expand and fluidizethe expansion flow layer, thereby eliminating bubbles or open poresgenerated in the expansion flow layer.
 8. The method for manufacturingsemiconductor device according to claim 7, wherein the expansion flowlayer is made of a polycrystalline silicon or an amorphous siliconcontaining at least one of boron, phosphorus and fluorine.
 9. The methodfor manufacturing semiconductor device according to claim 7, wherein theoxidation preventive layer is formed of a silicon nitride film.
 10. Themethod for manufacturing semiconductor device according to claim 7,wherein a pressure of the oxidation atmosphere in the expansion step isatmospheric pressure or more, and a heat treatment temperature is 400°C. to 800° C.